Epidemiological analyses of hospital admissions and mortality data have indicated that adverse human health effects are associated with present-day ambient particualte matter (PM) pollution levels. However, the PM mass measurement is chemically non-specific, ignoring the fact that the various particles (e.g. from differing source) may not have the same toxicity. A determinatio of PM's more toxic components would help elucidate possible mechanisms for the observed PM effects, and might allow State and Federal regulatory control efforts to more cost effectively achieve air pollution public health improvements.